EnumMap (Java 2 Platform SE 5.0) (original) (raw)

java.util

Class EnumMap<K extends Enum,V>

java.lang.Object extended by java.util.AbstractMap<K,V> java.util.EnumMap<K,V>

All Implemented Interfaces:

public class EnumMap<K extends Enum,V>

A specialized Map implementation for use with enum type keys. All of the keys in an enum map must come from a single enum type that is specified, explicitly or implicitly, when the map is created. Enum maps are represented internally as arrays. This representation is extremely compact and efficient.

Enum maps are maintained in the natural order of their keys (the order in which the enum constants are declared). This is reflected in the iterators returned by the collections views (keySet(),entrySet(), and values()).

Iterators returned by the collection views are weakly consistent: they will never throw ConcurrentModificationException and they may or may not show the effects of any modifications to the map that occur while the iteration is in progress.

Null keys are not permitted. Attempts to insert a null key will throw NullPointerException. Attempts to test for the presence of a null key or to remove one will, however, function properly. Null values are permitted.

Like most collection implementations EnumMap is not synchronized. If multiple threads access an enum map concurrently, and at least one of the threads modifies the map, it should be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the enum map. If no such object exists, the map should be "wrapped" using the Collections.synchronizedMap(java.util.Map<k, v="">)</k,> method. This is best done at creation time, to prevent accidental unsynchronized access:

 Map<EnumKey, V> m = Collections.synchronizedMap(new EnumMap(...));

Implementation note: All basic operations execute in constant time. They are likely (though not guaranteed) to be faster than theirHashMap counterparts.

This class is a member of the Java Collections Framework.

Since:

1.5

See Also:

EnumSet, Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map
Map.Entry<K,V>

Constructor Summary
EnumMap(Class<K> keyType) Creates an empty enum map with the specified key type.
EnumMap(EnumMap<K,? extends V> m) Creates an enum map with the same key type as the specified enum map, initially containing the same mappings (if any).
EnumMap(Map<K,? extends V> m) Creates an enum map initialized from the specified map.

Method Summary
void	clear() Removes all mappings from this map.
EnumMap<K,V>	clone() Returns a shallow copy of this enum map.
boolean	containsKey(Object key) Returns true if this map contains a mapping for the specified key.
boolean	containsValue(Object value) Returns true if this map maps one or more keys to the specified value.
Set<Map.Entry<K,V>>	entrySet() Returns a Set view of the mappings contained in this map.
boolean	equals(Object o) Compares the specified object with this map for equality.
V	get(Object key) Returns the value to which this map maps the specified key, or null if this map contains no mapping for the specified key.
Set<K>	keySet() Returns a Set view of the keys contained in this map.
V	[put](../../java/util/EnumMap.html#put%28K, V%29)(K key,V value) Associates the specified value with the specified key in this map.
void	putAll(Map<? extends K,? extends V> m) Copies all of the mappings from the specified map to this map.
V	remove(Object key) Removes the mapping for this key from this map if present.
int	size() Returns the number of key-value mappings in this map.
Collection<V>	values() Returns a Collection view of the values contained in this map.

Methods inherited from class java.util.AbstractMap
hashCode, isEmpty, toString

Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, [wait](../../java/lang/Object.html#wait%28long, int%29)

Constructor Detail

EnumMap

public EnumMap(Class<K> keyType)

Creates an empty enum map with the specified key type.

Parameters:

keyType - the class object of the key type for this enum map

Throws:

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if keyType is null

EnumMap

public EnumMap(EnumMap<K,? extends V> m)

Creates an enum map with the same key type as the specified enum map, initially containing the same mappings (if any).

Parameters:

m - the enum map from which to initialize this enum map

Throws:

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if m is null

EnumMap

public EnumMap(Map<K,? extends V> m)

Creates an enum map initialized from the specified map. If the specified map is an EnumMap instance, this constructor behaves identically to EnumMap(EnumMap). Otherwise, the specified map must contain at least one mapping (in order to determine the new enum map's key type).

Parameters:

m - the map from which to initialize this enum map

Throws:

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if m is not anEnumMap instance and contains no mappings

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if m is null

Method Detail

size

public int size()

Returns the number of key-value mappings in this map.

Specified by:

[size](../../java/util/Map.html#size%28%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[size](../../java/util/AbstractMap.html#size%28%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Returns:

the number of key-value mappings in this map

containsValue

public boolean containsValue(Object value)

Returns true if this map maps one or more keys to the specified value.

Specified by:

[containsValue](../../java/util/Map.html#containsValue%28java.lang.Object%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[containsValue](../../java/util/AbstractMap.html#containsValue%28java.lang.Object%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Parameters:

value - the value whose presence in this map is to be tested

Returns:

true if this map maps one or more keys to this value

containsKey

public boolean containsKey(Object key)

Returns true if this map contains a mapping for the specified key.

Specified by:

[containsKey](../../java/util/Map.html#containsKey%28java.lang.Object%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[containsKey](../../java/util/AbstractMap.html#containsKey%28java.lang.Object%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Parameters:

key - the key whose presence in this map is to be tested

Returns:

true if this map contains a mapping for the specified key

get

public V get(Object key)

Returns the value to which this map maps the specified key, or null if this map contains no mapping for the specified key.

Specified by:

[get](../../java/util/Map.html#get%28java.lang.Object%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[get](../../java/util/AbstractMap.html#get%28java.lang.Object%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Parameters:

key - the key whose associated value is to be returned

Returns:

the value to which this map maps the specified key, or null if this map contains no mapping for the specified key

See Also:

AbstractMap.containsKey(Object)

put

public V put(K key, V value)

Associates the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced.

Specified by:

[put](../../java/util/Map.html#put%28K, V%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[put](../../java/util/AbstractMap.html#put%28K, V%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Parameters:

key - the key with which the specified value is to be associated

value - the value to be associated with the specified key

Returns:

the previous value associated with specified key, ornull if there was no mapping for key. (A null return can also indicate that the map previously associatednull with the specified key.)

Throws:

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if the specified key is null

remove

public V remove(Object key)

Removes the mapping for this key from this map if present.

Specified by:

[remove](../../java/util/Map.html#remove%28java.lang.Object%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[remove](../../java/util/AbstractMap.html#remove%28java.lang.Object%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Parameters:

key - the key whose mapping is to be removed from the map

Returns:

the previous value associated with specified key, ornull if there was no entry for key. (A null return can also indicate that the map previously associatednull with the specified key.)

putAll

public void putAll(Map<? extends K,? extends V> m)

Copies all of the mappings from the specified map to this map. These mappings will replace any mappings that this map had for any of the keys currently in the specified map.

Specified by:

[putAll](../../java/util/Map.html#putAll%28java.util.Map%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[putAll](../../java/util/AbstractMap.html#putAll%28java.util.Map%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Parameters:

m - the mappings to be stored in this map

Throws:

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - the specified map is null, or if one or more keys in the specified map are null

clear

public void clear()

Removes all mappings from this map.

Specified by:

[clear](../../java/util/Map.html#clear%28%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[clear](../../java/util/AbstractMap.html#clear%28%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

keySet

public Set<K> keySet()

Returns a Set view of the keys contained in this map. The returned set obeys the general contract outlined inMap.keySet(). The set's iterator will return the keys in their natural order (the order in which the enum constants are declared).

Specified by:

[keySet](../../java/util/Map.html#keySet%28%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[keySet](../../java/util/AbstractMap.html#keySet%28%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Returns:

a set view of the keys contained in this enum map

values

public Collection<V> values()

Returns a Collection view of the values contained in this map. The returned collection obeys the general contract outlined inMap.values(). The collection's iterator will return the values in the order their corresponding keys appear in map, which is their natural order (the order in which the enum constants are declared).

Specified by:

[values](../../java/util/Map.html#values%28%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[values](../../java/util/AbstractMap.html#values%28%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Returns:

a collection view of the values contained in this map

entrySet

public Set<Map.Entry<K,V>> entrySet()

Returns a Set view of the mappings contained in this map. The returned set obeys the general contract outlined inMap.keySet(). The set's iterator will return the mappings in the order their keys appear in map, which is their natural order (the order in which the enum constants are declared).

Specified by:

[entrySet](../../java/util/Map.html#entrySet%28%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Specified by:

[entrySet](../../java/util/AbstractMap.html#entrySet%28%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Returns:

a set view of the mappings contained in this enum map

equals

public boolean equals(Object o)

Compares the specified object with this map for equality. Returnstrue if the given object is also a map and the two maps represent the same mappings, as specified in the Map.equals(Object) contract.

Specified by:

[equals](../../java/util/Map.html#equals%28java.lang.Object%29) in interface [Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Overrides:

[equals](../../java/util/AbstractMap.html#equals%28java.lang.Object%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Parameters:

o - the object to be compared for equality with this map

Returns:

true if the specified object is equal to this map

See Also:

Object.hashCode(), Hashtable

clone

public EnumMap<K,V> clone()

Returns a shallow copy of this enum map. (The values themselves are not cloned.

Overrides:

[clone](../../java/util/AbstractMap.html#clone%28%29) in class [AbstractMap](../../java/util/AbstractMap.html "class in java.util")<[K](../../java/util/EnumMap.html "type parameter in EnumMap") extends [Enum](../../java/lang/Enum.html "class in java.lang")<[K](../../java/util/EnumMap.html "type parameter in EnumMap")>,[V](../../java/util/EnumMap.html "type parameter in EnumMap")>

Returns:

a shallow copy of this enum map

See Also:

Cloneable

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.